CCDC42

CCDC42 is a coiled-coil domain-containing protein that localizes to the manchette, head-tail coupling apparatus (HTCA), and sperm tail during spermiogenesis, and to the centrosome in somatic cells (PMID:31475146). It physically interacts with ODF1, ODF2, CCDC38, CCDC146, and CFAP58, forming part of an intra-manchette/intraflagellar transport complex that delivers structural cargoes such as ODF2 to the assembling flagellum (PMID:31475146, PMID:35587122, PMID:38038747, PMID:38602507). Loss of CCDC42 in mice disrupts HTCA formation, abolishes flagellated sperm production, and causes male sterility, establishing it as essential for sperm head shaping and flagellum biogenesis (PMID:26945718).

1. 2016 High

   The first loss-of-function study established that CCDC42 is required for head-tail coupling apparatus formation and sperm flagellum development, resolving the question of whether this uncharacterized coiled-coil protein has an essential developmental role.

   Evidence Ccdc42 knockout mouse with histological/morphological analysis of testes and sperm showing absent flagella and HTCA defects

   PMID:26945718

   Open questions at the time

   • Subcellular localization of CCDC42 during spermiogenesis was not defined
   • No interacting partners identified
   • Mechanism by which CCDC42 loss disrupts HTCA was unknown
2. 2019 Medium

   Subcellular mapping placed CCDC42 at the manchette, HTCA, sperm tail, and somatic centrosome, and identified ODF1 and ODF2 as direct physical partners, situating CCDC42 within the cytoskeletal scaffold of spermatid-specific structures.

   Evidence Immunofluorescence in spermatids and somatic cells; co-immunoprecipitation/pulldown with ODF1 and ODF2

   PMID:31475146

   Open questions at the time

   • ODF1 and ODF2 interactions shown by single Co-IP/pulldown without independent reciprocal validation in a second laboratory
   • Functional consequence of CCDC42–ODF interactions not tested
   • Whether CCDC42 acts in transport versus as a structural anchor was unresolved
3. 2022 Medium

   Identification of CCDC38 as a CCDC42 interactor, combined with the CCDC38 knockout phenotype (manchette distortion, MMAF, reduced ODF2 transport), placed CCDC42 within an intra-manchette/intraflagellar transport complex required for cargo delivery to the flagellum.

   Evidence Co-immunoprecipitation of CCDC42–CCDC38; Ccdc38 knockout mice with immunofluorescence and western blot

   PMID:35587122

   Open questions at the time

   • Direct transport function of CCDC42 itself (versus scaffolding) not distinguished
   • Stoichiometry and order of assembly of the CCDC42–CCDC38–IFT complex unknown
   • Whether CCDC42 loss phenocopies CCDC38 loss at the molecular cargo level was untested
4. 2023 Medium

   CCDC146 was added to the CCDC42-containing network, and structural modeling of the CCDC146–CCDC42 interface together with the Ccdc146 knockout phenotype refined the picture of a modular CCDC38–CCDC42–CCDC146–IFT complex for flagellum biogenesis.

   Evidence Co-immunoprecipitation, computational interaction modeling with experimental validation, Ccdc146 knockout mice

   PMID:38038747

   Open questions at the time

   • No high-resolution experimental structure of the complex exists
   • Whether CCDC42 directly contacts IFT particles or only through CCDC38/CCDC146 is unresolved
   • Functional redundancy among coiled-coil subunits not tested
5. 2024 Medium

   CFAP58 was identified as another CCDC42 interactor that stabilizes CCDC42 protein levels at the manchette, indicating upstream regulation of CCDC42 within the IMT/IFT pathway.

   Evidence Co-immunoprecipitation of CFAP58–CCDC42; Cfap58 knockout mice showing reduced manchette CCDC42 levels

   PMID:38602507

   Open questions at the time

   • Single Co-IP in one laboratory; independent confirmation pending
   • Mechanism of CFAP58-mediated stabilization (e.g., protecting from degradation vs. promoting localization) is unknown
   • Whether CFAP58 loss fully recapitulates CCDC42 loss phenotype not shown

• Key open questions include the precise cargo-binding mechanism of CCDC42, the atomic structure of the full manchette transport complex, whether CCDC42's centrosomal localization in somatic cells reflects a non-reproductive function, and whether human CCDC42 mutations cause male infertility.
• No human genetic data linking CCDC42 variants to infertility
• No reconstituted biochemistry of the CCDC42-containing transport complex
• Somatic (centrosomal) function of CCDC42 entirely unexplored